The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent to an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
However, the further miniaturization of the various components, particularly, the size and/or pitch of magnetic grains, presents its own set of challenges and obstacles in conventional products. Noise performance and spatial resolution are key parameters in magnetic recording media and are ongoing challenges to advance the achievable areal density of media. The dominant media noise source today is transition jitter. In sputtered media, it reflects the finite size, random positioning and dispersions in size, orientation and magnetic properties of the fine grains that comprise the media.
HAMR, also referred to as thermally assisted magnetic recording, has emerged as a promising magnetic recording technique to address grain size and transition jitter. As the coercivity of the ferromagnetic recording material is temperature dependent, HAMR employs heat to lower the effective coercivity of a localized region of the magnetic media and write data therein. The data state becomes stored, or “fixed,” upon cooling the magnetic media to ambient temperatures (i.e., normal operating temperatures typically in a range between about 15° C. and 60° C.). Heating the magnetic media may be accomplished by a number of techniques such as directing electromagnetic radiation (e.g. visible, infrared, ultraviolet light, etc.) onto the magnetic media surface via focused laser beams or near field optical sources. HAMR techniques may be applied to longitudinal and/or perpendicular recording systems, although the highest density storage systems are more likely to be perpendicular recording systems.
HAMR thus allows use of magnetic recording materials with substantially higher magnetic anisotropy and smaller thermally stable grains as compared to conventional magnetic recording techniques. Moreover, to further increase the areal density of magnetic recording media, granular magnetic recording materials may be utilized. Granular magnetic recording materials typically include a plurality of magnetic grains separated by one or more segregants, which aid in limiting the lateral exchange coupling between the magnetic grains. These segregants may influence magnetic properties, the size and shape of the magnetic grains, the exchange coupling strength between the magnetic grains, the grain boundary width, etc.